Free-to-play business models may be on the rise, but subscription-based models are still holding strong thanks largely to that $1 billion juggernaut called World of Warcraft. It also helps that even subscription-based MMOs are making a killing with microtransactions. So despite the MMO subscription market shrinking year-over-year since 2010, part of the decline has been offset by microtransactions, nearly doubling from 14% to 27% in the past five years. In fact, though the market has shrunk from 30.6 million monthly active subscribers to 23.4 million, the average revenue per user has actually risen. The user base may be lower, but the ones that remain are loyal and willing to spend.

World of Warcraft unsurprisingly tops the 2013 list with 36% of the market, raking in worldwide revenues of $1.041 billion. What may be surprising to some is that the next four contenders all earned more than $100 million in 2013: 1998's Lineage captured 9% of the market and earned $253 million; TERA: Online captured 8% of the market and earned $236 million; Star Wars: The Old Republic captured 6% and earned $165 million; and Lord of the Rings Online captured 4% of the market and earned $104 million. Not too shabby at all. In total, subscription-based MMOs earned $2.882 billion in worldwide revenues in 2013.

It'll be interesting to see how 2014 plays out with two big new entries in the subscription market, Bethesda's Elder Scrolls Online and NCsoft's Wildstar. Elder Scrolls Online boasts a subscriber base of 772,374 as of June, likely helped by its multi-platform release. Meanwhile, NCsoft not only has Lineage under its publishing arm, but it also has three other MMOs in the 2013 Top Ten (Aion, Blade and Soul, and Lineage II) – so there are certainly big expectations for Wildstar as well. While free-to-play is certainly on the rise, it doesn't seem like subscription-models are going away any time soon, even if some are merely optional.